row_number() over()分组排序功能 partition by 用于给结果集分组

select * from (

        select   row_number() over(partition by Gid order by Gid ASC) as RowN, *

        from(

        select b.Gid, a.OrderNo,b.Carcode from  fit_CarOrder a inner join  Fit_CarDetail b

        on a.OrderNo=b.DetailNo

        inner join  Fit_OrderDetail  c on a.Gid=c.OrderGid

        where a.orderno=''

        ) as bb)

        as tt  where  tt.RowN=1

分组排序对于主单对应多个明细 分组排序去重  如果 明细中对应到第三个明细中也存在对应的主单信息时 最好取决于第二个表的明细ID来排序分组筛选重复项